The objective of our proposed research is to study red cell membrane-membrane and membrane-artificial surface adhesion and to evaluate the intrinsic role of membrane rigidity (shear and bending) in the adhesion process. The research will provide the first measurements of the work of formation of the interfacial contact area. Also, the ultimate strength of the adhesive contact will be measured; this is important since it appears that the adhesion process is often not (thermodynamically) reversible. Contact between red cell membranes, red cell membrane and phospholipid vesicle membrane, and red cell membrane and coated microsphere surfaces will be studied. The adhesion process will be mediated by a variety of agents: fibrinogen, dextran, small charged liposomes (simulating "virus-like" bodies), polylysine, and lectins (e.g., conconavalin A). The deformation responses of red cell membranes to environmental forces is predominantly governed by the in-plane elastic properites, i.e., area dilation modulus and surface extension (shear) modulus, which have been studied. However, the bending or curvative elastic modulus (which is important in regions where the contribution of membrane tensions to equilibrium is small) has not been measured. From the observation of the characteristic dimension for the region influenced by bending rigidity as a function of membrane tensions, the magnitude of the bending modulus and the effect on the adhesion process will be determined. Membrane adhesion and deformation will be produced with micromanipulation of human red cells, large phospholipid vesicles, and small microspheres. The methods involve dual micropipet techniques, and the observations are recorded with a video-microscopic system. Micropipet aspiration of a flaccid red cell is used as a transducer for the direct measurement of the work of forming interfacial contact and is used to measure the ultimate strength of the adhesive contact.